breed [wolves wolf]
breed [awolves awolf]


turtles-own
[
  partner   ;;  the turtle that is our partner, or "nobody" if we don't have one
]

;;  This procedure will setup 150 turtles, by randomly placing them around the world.
to setup
  clear-all
  ;create-turtles 150
  set-default-shape wolves "wolf"
  create-wolves initial-no-wolves 
  [
    ;;  turtles get random coordinates, and they are
    ;;  light gray (to show they don't have partners yet).
    set color brown
    set size 1.5  ;; easier to see
                  ;;set energy random (2 * wolf-gain-from-food)
    setxy random-xcor random-ycor
    set partner nobody
  ]
  set-default-shape awolves "awolf"
  create-awolves initial-no-wolves 
  [
    ;;  turtles get random coordinates, and they are
    ;;  light gray (to show they don't have partners yet).
    set color yellow
    set size 1.5  ;; easier to see
                  ;set energy random (2 * wolf-gain-from-food)
    setxy random-xcor random-ycor
    set partner nobody
  ]
  
  reset-ticks
end

;; have each turtle move until they find a partner at which point they turn red
to find-partners
  let singles_wolf wolves with [partner = nobody]
  let singles_awolf awolves with [partner = nobody]
  let partner_wolves awolves with [partner != nobody]  
    ;;  In this example, only turtles that haven't found a partner can move around.
    ask singles_wolf
    [
    ;;  Randomly move about the world
      lt random 40
      rt random 40
      fd 1
    ]
    
    ask singles_awolf
    [
      ;;  Randomly move about the world
      lt random 40
      rt random 40
      fd 1
    ]
    
    ask partner_wolves 
    [
      
      let xcoord xcor
      let ycoord ycor
      setxy xcoord ycoord 
      let move_pos random 10
      lt move_pos
      rt move_pos
      fd 1
      ask partner [
        setxy xcoord ycoord
        lt move_pos
        rt move_pos
        fd 1
      ]
       
    ]
    
    ;;  Now that all unpartnered turtles have moved, ask the unpartnered turtles to check if they
    ;;  are on a patch with a turtle that also don't have a partner.
    ask awolves
    [
      if (partner = nobody) and (any? other wolves-here with [partner = nobody])
      [
        ;;  There could be more than one partner to choose from, so we use one-of
        ;;  to randomly choose one of the turtle without a partner
        set partner one-of other wolves-here with [partner = nobody]
        
        ;;  We graphically show that we have a partner by turning red.
        let pcolor_val  random 10 * red - 2 + random 7
        set color pcolor_val
 
        ask partner [
        ;; Ask our partner to partner with ourselves.
          set partner myself
          ;;  Color my partner red too
          set color pcolor_val
        ]
      
      ]
    ]
    
    ;;  As a check on the correctness of the code, let's make sure that
    ;;  the partner assignments are consistent.
    
    tick
end


; Public Domain:
; To the extent possible under law, Uri Wilensky has waived all
; copyright and related or neighboring rights to this model.
@#$#@#$#@
GRAPHICS-WINDOW
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BUTTON
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find-partners
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MONITOR
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SLIDER
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@#$#@#$#@
## WHAT IS IT?

This code example shows how agents can "partner up" with each other.  Each turtle will pair up with another turtle.  Each turtle in a pair are aware of this partnership, preventing mismatched partners and multiple partners.

In this example, the turtles needs to be on the same patch to form a partnership, but you can easily change it to be turtles within a given radius (by using `in-radius`), or using no spatial requirements at all.

Pairing turtles is used by many models that require single turtle interactions.  One example is models that require turtles to reproduce with another turtle.  Another example is the GasLab models where molecules are forced to only interact with one other molecule at time, which simplifies the code by preventing a three (or more)-way collision.

## HOW IT WORKS

Turtles with no partner are gray; partnered turtles are red.  Unpartnered move randomly about the View until they land on a patch with another unpartnered turtle.  When this happens, the two turtles form a partnership and stop moving.

## RELATED MODELS

Grouping Turtles Example shows how to form groups that contain more than two turtles.
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@#$#@#$#@
NetLogo 5.0
@#$#@#$#@
setup
repeat 86 [ find-partners ]
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@#$#@#$#@
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